The present invention relates to rotary fluid pressure devices such as low speed, high torque gerotor motors, and more particularly, to an improved case drain flow path arrangement for such a motor.
A typical motor of the type to which the present invention relates includes a housing defining an inlet port and an outlet port, and some sort of fluid energy-translating displacement mechanism such as a gerotor gear set. The motor further includes stationary valve means communicating with the volume chambers of the displacement mechanism, and a rotary valve member which provides communication between the ports and the stationary valve member.
Some motors of this type have a rotary valve which is referred to as a "fixed clearance valve", because the valve member is disposed between the stationary valve member and a fixed surface defined by the housing. Other motors of the type to which the invention relates are not fixed clearance, but instead, include some form of valve seating mechanism which biases the rotary valve member into engagement with the stationary valve member, and at the same time, separates the pressurized fluid from the return fluid.
Although the present invention may be used in a motor having either type of valving described above, it is especially advantageous when used in a motor having a valve seating mechanism, and will be described in connection therewith.
During normal operation of a gerotor motor, there is a certain amount of leakage of pressurized fluid from the gerotor gear set to a central case drain region of the motor. It is desirable to communicate this leakage fluid to the low pressure port to prevent the buildup of excessive fluid pressure on the shaft seals. This leakage fluid is typically used to lubricate certain elements of the motor which are subjected to substantial wear, such as the drive shaft connections and the bearings.
In the prior art motors of this type, such as shown in U.S. Pat. No. 3,572,983, communication of leakage fluid from the case drain region to whichever of the ports was connected to system reservoir was typically accomplished by means of a pair of check valve assemblies. In this arrangement, pressurized fluid would keep one of the check valves closed, while the other check valve would be subject only to return pressure, and slightly pressurized leakage fluid would unseat the check valve at low pressure and flow to the motor outlet. As is well known to those skilled in the art, such a check valve arrangement is necessitated by the fact that motors of this type are almost always required to be bidirectional, i.e., either port can be pressurized, depending upon the desired direction of rotation of the output shaft. The prior art check valve arrangement will be described in greater detail subsequently in the specification of the present application.